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Basic Concepts of Chemistry Online Mcqs Test

Maan AliLast Updated: October 14, 2025

Important Basic Concepts of Chemistry Question and Answer

Total Questions:	71
Time Allowed:	30 Minutes
Total Marks:	71
How to Attempt Test:	Please choose the right Option in MCQ-type question.
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Basic Concepts of Chemistry Practice Test Online With Explanation

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Page 1 of 3

1. What is the net charge on ferrous ion?

2. Difference in density is the basis of

Molecular attraction

Ultrafiltration

Molecular sieving

Gravity separation

3. Which of the following is NOT a pure substance?

Soil

Gold

Water

Sodium Chloride

4. The coefficient of viscosity η of a fluid moving steadily between two surfaces is given by the formula, f = η dV/dx where f is the frictional force on the fluid. A is an area in the fluid and dV/dx is the velocity gradient inside the fluid at that area. The S.I. unit of viscosity coefficient η is given as,

Kg m¯¹s¯¹

Nil, it is dimensionless constant

Newton

Nm¯²s¯²

5. Calculate the number of moles of CaCO₃ (Formula weight = 100) in a sample that weighs 25.0 grams.

0.25

0.75

0.5

1.00

6. 1 mole of CH₄ contains

6.02 x 10²³ atoms of H

1.81 x 10²³ molecules of CH₄

4 g-atom of hydrogen

3.0 g of carbon

7. What does the atomic number of an atom represent?

Protons and electrons

Protons and neutrons

Neutrons and electrons

Electrons and shells

8. Molecular compounds can be found in all three states of matter at room temperature. Which molecule compound is a liquid at room temperature?

Carbon dioxide

Water

Sugar

Methane

9. Most atoms are neutral, to become a positive ion the atom must:

Lose electrons and protons

Gain electrons and protons

Lose electrons

None of these

10. Among the following pairs, the one which illustrates the law of multiple proportions is

CS₂, FeSO₄

H₂S, SO₂

CuO, Cu₂O

NH₃, HC1

11. A ring contains 1.2g of diamond. How many number of carbon atoms are in diamond?

6.02 x 10²³

6.02 x 10²²

3.01 x 10²²

3.01 x 10²³

12. How many moles of CO₂ are present in 220 mg?

5000 mole

0.005 mole

10 moles

5 moles

13. What is the percent water in hydrated calcium chloride (CaC1₂ 2H₂O)?

24.51%

12.26%

66.67%

32.47%

14. The prefix 10¹⁸ is

Giga

Exa

Kilo

Nano

15. Ayesha required an aqueous solution of sodium chloride. She made the solution by dissolving salt in:

Vinegar

Water

Oxygen gas

Air

16. What are the ratios among the volumes of gases of ³²O₂,²H₂, and ¹⁶CH₄ if equal mass of each gas is taken?

1:1:1

1:16:2

2:16:2

2:16:1

17. An oxide of nitrogen contain 36.8% nitrogen and 63.2% oxygen by mass. Calculate its empirical formula.

N₂O

NO₂

N₂O₃

18. Since atoms are neutral, the number of electrons is equal to the number of:

Protons

Neutrons

Nucleus

Ions

19. Vapor density of a gas is 22. What is its molecular mass?

20. Which of the following represents an element?

A pure substance made up of two or more types of atoms

The periodic table

A pure substance made up of one type of atom

A compound made up of one type of element

21. Which of the following method is used to estimate oxygen in an organic compound?

Combustion method

Duma’s method

K. Jeldahl’s method

All of above

22. Which of the following is NOT true of matter on the Earth?

Matter always consists of molecules

All matter contains chemical elements

All substances are made of matter

Matter is always composed of atoms

23. What are the parts of an atom?

Protons, neutrons, electrons, nucleus

Protons, neutrons, nucleus, mass

Ions, electrons, neutrons, water

Nucleus, element, carbon, space

24. Empirical formula of chloroform is

CH₃cl

CH₂C₁₂

CHCl₃

CHCl

25. A compound contains 6.0 g of carbon and 1.0 g of hydrogen. The percent composition of the compound is:

83% hydrogen and 17% carbon

14% hydrogen and 86% carbon

86% hydrogen and 14% carbon

17% hydrogen and 83% carbon

Page 2 of 3

26. Which of the following represents a compound?

Two words in one word

A pure substance made up of one type of atom

Pure substances made up to of 2 or more types of atoms

Made up of 10 atoms

27. Which of the following statements is FALSE for the chemical equation given below in which nitrogen gas reacts with hydrogen gas to form ammonia gas assuming the reaction goes to completion?
N₂ + 3H₂ → 2NH₃

The reaction of one mole of H₂ will produce 2/3 moles of NH₃.

The reaction of three moles of hydrogen gas will produce 17 g of ammonia

One moles of N₂ will produce two moles of NH₃.

One molecule of nitrogen requires three molecules of hydrogen for complete reaction.

28. Which of the following statements is wrong about isotopes?

They possess same position in the periodic table

They possess same chemical properties

They possess same physical properties

They possess different mass number

29. If the empirical formula of compound is CH₂. Which of the following is true about its molecular formula?

Only one molecular formula (C2H2) is possible

Only one molecular formula (CH2) is possible

Its molecular formula does not exist

More than one could be a molecular formula for CH₂

30. How will you separate a mixture of two gases?

Fractional distillation technique

Chromatography

Osmosis

Graham’s law of diffusion technique

31. The volume occupied by 28 gram of N₂ at STP?

1.12 dm³

22.4 dm³

112 Cm³

2.24 dm³

32. How many moles of KBrO₃ are required to prepare 0.0700 moles of Br₂ according to the reaction: KBrO₃ + 5KBr + 6HNO₃ → 6KNO₃ + 3Br₂ + 3H₂O

0.0233

0.210

0.0704

0.0732

33. The Number of oxygen atoms in 4.4 g of CO2 is approximately

1.2 x 10²³

6 x 10²²

12 x 10²³

6 x 10²²

34. Water (H₂O) is a common compound made up of:

3 elements and a total of 3 atoms

2 elements and a total of 3 atoms

2 elements and a total of 2 atoms

3 elements and a total of 2 atoms

35. Which one of the following is ambiguous?

A mole of potassium ions

A mole of electrons

A mole of sodium atoms

A mole of hydrogen

36. The empirical formula of a compound is CH₂O and its molecular mass is 120. The molecular formula of the compound is

C₃H₆O₃

CH₂O

C₄H₈O₄

C₂H₄O₂

37. What is a chemical compound?

A combination of two protons and two electrons

A subatomic particle

A combination of two or more chemical elements

A mixture of two or more substance

38. How many moles of Helium gas occupy 22.4 L at 0°C at 1 atm. Pressure?

0.11

1.0

0.90

1.11

39. The empirical formula of the compound having 50% sulphur and 50% oxygen by mass is

SO₃

SO₂

S₂O₃

40. How many elements are present in two molecules of aspirin? The formula for aspirin is C₉H₈O₄.

41. One of the substances is used to absorb CO₂ gas in combustion analysis. Which is that substance?

KOH

SiO₂

Al₂O₃

Mg(ClO₄)₂

42. Irrespective of the source, pure sample of water always yields 88.89% mass of oxygen and 11.11% mass of hydrogen. This is explained by the law of

Multiple proportions

Conservation of mass

Definite proportions

Constant volume

43. Calculate the weight, in grams, of one molecule of carbon dioxide, CO₂.

1.99 x 10¯²³

1.37 x 10²²

4.65 x 10¯²³

7.31 x 10¯²³

44. For which of the following terms empirical formula cannot be applied?

It can be applied to all

CC1₄

NaC1

H₂O

45. Which of the following could be an empirical formula?

BaO₂

C₆H₁₂O₆

H₂O₂

C₂H₄

46. What do you call pure substances that are formed from the attraction between positive ions and negative ions?

Ionic element

Ionic charges

Ionic atoms

Ionic compounds

47. The compound having highest percent of oxygen is

CH₃COCH₃

H₂O

CH₃COOH

C₂H₅OH

48. An anhydrous salt of copper is found to contain 52.7% chlorine and 47.3% copper by mass. What is the empirical formula for this salt?

Cu₂Cl₃

CuCl₃

CuCl

CuCl₂

49. What is a multivalent ion?

Some ions can have only one charge

Only negatively charged

Ions that are made of more than one type of atom and act as one

An ion that can have more than one charge

50. How can you separate the mixture of two gases of different atomic masses?

Graham’s Law of diffusion

Sublimation

Chromatography

Crystallization

Page 3 of 3

51. To differentiate between C-12, C-13 and C-14, the instrument that you would use is

Infra-red spectrometer

Mass spectrometer

Ultraviolet spectrometer

Atomic absorption spectrometer

52. Indicate the incorrect statement form the following

Actual yield is always less than theoretical yield

Stoichiometric calculation can only be done if no side reaction happen

A limiting reactant is used at the end of reaction

The empirical and molecular formula of some of the compounds are same

53. What are the two different types of ions?

Polyatomic and multivalent

Electrons and protons

Polyatomic and compound ions

Negative and positive

54. The percentage of oxygen in NaOH is

55. Which of the following is a pure substance made up of two or more types of atoms or elements?

Compound

Mixture

Crystal

Element

56. Copper (II) oxide is mixed with organic compound during combustion. The purpose is

To reduce the time for completion of the reaction

To carry out compete combustion

All of these

To reduce the economy of the process

57. A gaseous mixture contains 50% helium and 50% methane by volume. What is the percent by weight of methane in the mixture?

19.97%

80.03%

50%

20.05%

58. Bromine has two isotopes having the relative abundances as ⁷⁵₃₉Br = 50.51% and ⁸¹₃₅Br= 49.49%. The average atomic mass of bromine is

79.5

59. Diameter of an atom is in the range of

0.2 Pm

2 x10¯¹⁰

0.2 nm

0.2 m

60. The hydrogen phosphate of certain metal has formula MHPO₄. The formula of metal chloride would be

M₂C1₂

MCL₂

MC1

MC1₃

61. If Na is Avogadro’s number, then number of valence electrons in 4.2 g of nitride ions N³¯ is

1.6 Na

2.4 Na

4.2 Na

3.2 Na

62. What is correct relationship between empirical and molecular formulas?

Empirical formula /n = Molecular formula

Empirical formula x √n = Molecular formula

Molecular formula /n = Empirical formula

Empirical formula x n² = Molecular formula

63. How do you calculate the number of neutrons in an atom?

The atomic mass plus the number of electrons

The atomic mass subtracted the number of protons

The atomic mass subtracted the number of electrons

The atomic mass plus the number of protons

64. How many number of ions are there in 98 grams of sulphate ions?

6.02 x 10²³

4 x 6.02 x 10²³

3 x 6.02 x 10²³

6.02 x 10²³ x 2

65. The set of numerical coefficients that balances the chemical equation K₂CrO₄ + CH1 → K₂Cr₂O₇ + KC1 + H₂O

2, 2, 1, 1, 1

1, 1, 2, 2, 1

2, 2, 1, 2, 1

2, 1, 1, 2, 1

66. Which of the following is an element?

Common Salt

Gold

Water

Sugar

67. Which law directly explains the law of conservation of mass?

Moley’s law

Newton’s law

Dalton’s law

Hund’s rule

68. Percent of calcium in calcium carbonate is

80%

20%

40%

30%

69. Balance the following equation using minimum integral coefficients: (NH₃ + O₂ → NO₂ + H₂O) Find the stoichiometric coefficient for oxygen gas O₂:

70. Isotopes differ in the

Number of neutrons

Number of protons

Number of atoms

Number of electrons

71. The modern atomic weight scale is based on

C¹²

O¹⁶

C¹³

H¹

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Maan AliLast Updated: October 14, 2025

33 Comments

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October 26, 2022 at 2:22 pm

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October 26, 2022 at 1:52 pm

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October 12, 2020 at 4:43 pm

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Momo says:

December 9, 2018 at 11:24 am

Mass of one mole of iodine is 254g not 245g. (127*2=254g)

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Basic Concepts of Chemistry Online Mcqs Test

Important Basic Concepts of Chemistry Question and Answer

Basic Concepts of Chemistry Practice Test Online With Explanation

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